Countless materials and structures are exposed to the environment and are thus affected by temperature. Temperature extremes such as high temperatures or low temperatures can impair long-term durability of materials, but also can lead to undesirable environmental impacts, such as heat island effects and volatile gas emissions. Temperature fluctuations can also lead to high energy consumption and HVAC cost for buildings, vehicles (including electrical vehicles, where HVAC consumes electricity and significantly reduces the mileage ranges). Non-limiting examples of suitable structures or materials that could benefit from thermal management could include, but are limited to, asphalt or pavement; building materials, such as roofing material, siding, and building envelopes; and vehicles, etc.
Many materials, due to their composition or structure, are prone to solar absorption which leads to relatively high surface temperatures.
Thermochromic materials have been added to asphalt binders as solar reflectors in order to modulate surface temperature of asphalt pavement. Discussions regarding the same are set forth in (Hu and Yu 2013a, 2013b):    Hu, J. Y. and Yu, X. (2013a). Experimental Study of Sustainable Asphalt Binder: Influence of Thermochromic Materials, Transportation Research Record, Issue Number: 2372, pp 108-115.    Hu, J. Y. and Yu, X. (2013b). Innovative Chromogenic Materials for Pavement Life Extension: Modeling Study of Surface Temperature of Sustainable Asphalt Pavement, International Journal of Pavement Research and Technology, March 2013, Volume 6, Issue 2, pp 141-146.
Temperature plays a major role on asphalt durability under both hot and cold weather conditions (Shami et al. 1997). For example, Huang et al. (2008) showed that the rutting typically occurred when the surface temperature of asphalt pavement is above 20° C.; the higher the surface temperature the higher the potential of rutting occurrence. Increase of surface temperature by 10° C. accelerated permanent plastic strain by 40 times. On the other side, low temperature crack is a major pavement distress in cold regions.
The black color of conventional asphalt corresponds to large solar absorbance and large emissivity. This makes it warm up fast under solar radiation and cool down fast under sudden temperature drop. Studies (Santamouris et al. 2007, Synnefa et al. 2008, Doulos et al. 2004) measured the surface temperature of asphalt pavement as high as 48-67° C. during summer. The elevated temperature during summer impacts durability of asphalt pavement by accelerating various distresses (i.e., rutting, bleeding, shoving, aging, fatigue damage) (Yoder and Witzak 1975). The high surface temperature also exacerbates the urban heat island effects and accelerates volatile emission. Cool pavement technology has been proposed that use materials with high reflectivity to solar radiation. Studies (Pomerantz et al. 2000, 2004) show that cool pavement, which features low surface temperatures, increases the service life of pavements. However, as the conventional cool pavement technologies reduce the surface temperature of pavement regardless of the season, the reduced temperature of asphalt pavement exacerbates the problem with low temperature cracking during the winter period (Hao et al. 2000, Kanerva and Zeng 1994). Besides, the lower surface temperature is inductive to ice formation, which impairs road safety and winter road maintenance. Similar issues are found for common types of cool roof technologies, which while reduce the energy consumption during summer but increase the energy consumption during winter, and therefore increase energy consumption for buildings located in heating dominant regions.
The temperature of the road surface is affected by three major thermal exchange mechanisms: absorption of the incident solar energy, thermal radiation to the atmosphere, and thermal convection with the air close to the roads surface. The direct source of heat for pavement comes from solar radiation. The surface temperature on roads can be unpleasantly high during summer (EPA 2009). Solar Reflectance (SR)/Solar Absorbance (SA), or the percentage of solar energy reflected/absorbed by a surface, are the main determinant of a material's maximum surface temperature. Thermal Emittance (SE) determines how much heat it will radiate per unit area at a given temperature. Using the thermal transfer model by NIST (Bentz 2000), it was shown that when the ambient temperature is within 3 degrees below the surface temperature, the heat loss by thermal radiation/emission is the dominant factor over the heat loss by convection. Solar Reflectance has a major role on the maximum surface temperature while Thermal Emittance determines the minimum temperature (Levinson et al. 2002).
Among these two important properties, there are only limited options to change the thermal emittance because most pavement materials inherently have high emittance values. Changing the solar reflectance can have a major impact on the surface temperature of pavements. Golden and Kaloush (2004) showed that at the same solar input, changing the solar reflectance value from that of ordinary asphalt to that of concrete will result in at least 10 degree drop in the road temperature. This means a significant reduction of rutting, aging, and emission of volatiles from asphalt roads.
In view of the above, there is still a need for thermochromic coatings having relatively high solar reflectance when subjected to relatively high temperatures and lower solar reflectance when subjected to lower temperatures. In addition, economical coating materials are also sought by industry.